The present invention relates to a self-contained heavy duty constant force sliding sash counterbalance assembly which embodies as the functional component a stacked plurality of constant force spring elements and is particularly suitable for use as either original equippage or retrofit in counterbalancing the larger and heavier vertically sliding sash construction, and gives the advantageous feature of providing a uniformily constant counterbalancing force over the operational opening range of the sash.
Typical of the spring operational counterbalance assemblies for heavy window sash constructions is that teaching as exemplified in U.S. Pat. No. 3,358,403 to Dinsmore, dated Dec. 19, 1967, which employs the combination of a standard coil spring with a compound pulley arrangement in order to gain a mechanical advantage in accommodating the counterbalance capability to the sash weight. And, in more current versions of the Dinsmore type assembly, a clustered plurality of coil springs may be used to achieve the necessary and desired counterbalance effect. However, although this type of mechanical combination does provide a true offsetting counterbalance capability, it is so functional at only one particular setting of sash opening within the overall range of sash opening possibilities, and at all other sash opening settings it is either substantially in excess of, or less than,that counterbalance force suitably needed.
The use of single constant force coil springs as sash counterbalance means in lighter window constructions is well known, being incorporated as integral components of the overall sash-and-frame construction. Typical exemplary teachings illustrating the foregoing would be as respectively set forth in U.S. Pat. No. 2,609,193 to Foster, dated Sep. 2, 1952, and U.S. Pat. No. 3,475,865 to Arnes, dated Nov. 4, 1969. And, in the case of employment of a constant force coil spring as the sash counterbalance means, a substantially constant counterbalance force is achieved over the opening range of the sash and at all settings therebetween.
The employment of dual constant force coil springs is also taught, which embodiment is primarily for purposes of spring stabilization to prevent rocking and twisting of the extended coil ribbons during use. Exemplary of the dual constant force coil spring sash counterbalance teachings are those as set forth respectively in U.S. Pat. No. 2,635,282 to Trammell, Sr., et al, dated Apr. 21, 1953, and U.S. Pat. No. 3,992,751 to Foster et al, dated Nov. 23, 1976.
The current invention is distinguished over the previous teachings in that it provides a new and novel constant force spring counterbalance assembly of unitized construction, which in turn provides advantages and features as more specifically hereinafter detailed and set forth.